Semiconductor nanocrystals are very small crystallites of semiconductor material, also known as quantum dots, which have the opto-electronic properties of semiconductors. They are typically prepared as colloids, and as such, display physico-chemical properties of molecules. One feature of semiconductor nanocrystals is that their color may be controlled by their size because of quantum confinement on their electronic states. The electron occupation of the nanocrystals can be controlled by n- and p-type doping as is common for bulk semiconductors.
For example, Mn-doped semiconductor nanocrystals exhibit unique optical and magneto-optical properties. Large Zeeman effects are observed in Mn-doped ZnS, ZnSe and CdSe nanocrystals, and the effects indicate that quantum-confined excitons feel a large effective magnetic field of up to 400 Tesla, induced by the presence of a few Mn2+ ions inside the nanocrystals. Spin-polarizable excitonic photoluminescence (PL) is observed in Mn-doped CdSe nanocrystals. Additionally, Mn dopants can introduce new luminescence properties to nanocrystals. Mn-doped CdS/ZnS core/shell nanocrystals possess dopant-position-dependent PL properties. Mn dopants can be used as a radial pressure gauge to measure the lattice strains in the nanocrystals. Mn-doped CdS/ZnS core/shell nanocrystals display dual emission properties.
With respect to PL properties of Mn-doped nanocrystals, when a photon is absorbed by a Mn-doped nanocrystal, an electron-hole pair (i.e., exciton) is created and confined inside the nanocrystal. These doped nanocrystals have multiple modes of energy release and means for selectively or differentially addressing these modes of release, in principle allow the tuning of properties. Newly discovered optical properties of dual emitting doped semiconductor nanocrystals have the potential to expand the technologies that can be addressed by these compositions of matter. Such properties allow manipulation of the dual emitting doped nanocrystal's optical emission in a manner that can be readily and rapidly switched, unlike properties defined solely by their size, composition or doping level, which are effectively fixed upon preparation. Because of these properties, doped nanocrystal can be technologically exploited in fields including, displays, biomedical diagnosis, and in vivo biological imaging.